Behavior: Genes and Behavior

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mct
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241477
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Behavior: Genes and Behavior
Updated:
2013-10-19 13:12:54
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Lecture Four
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L:4 Genes and Behavior
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  1. Single gene effects on behavior
    • Relatively rare (as usually more than one gene involved in behavior) but relatively easy to study
    • Eg. hygienic and non-hygienic honey bees: bacteria (American foul brood) that attacks bee larvae.  Hygienic colonies worker bees will uncap a cell in the colony if dead larva or pups are remove the corpse, non-hygienic colonies workers do not.
  2. Types of transgenics
    • "knockout" - a gene is removed or rendered inactive
    • "knockin" a novel gene is inserted
    • "conditional" the promoter for a gene is altered so that it can be switched on or of by the experimenter
  3. Polygenic effects
    • Most phenotypic characters are not associated with a specific gene but are the result of numerous genes interacting (polygenic)
    • These effects are far harder to study, because many genes may have a small but important effect on phenotype
    • Do not follow Medalian laws of inheritance
    • Lots of work currently being done on quantitative genomics to id important genes for growth, development and disease susceptibility
  4. Pleiotrophy
    • Allele has more than one effect on the phenotype
    • Yellow allele in Drosophila: slower at matting, yellow strips on the body
    • Norm rather than the exception
    • Change in one enzyme likely to affect several pathways and phenotypic characters
  5. Demonstrating genetic effects on behavior
    • Approaches to demonstrate genetic effects on Behaviour all involve linking behavior variation to genetic differences
    • 1. using "natural" behavioral variation
    • 2. using selective breeding
    • 3. Using strain differences
  6. Natural species-species behavioral variation
    • Interbreed closely related species with different patterns of behavior to study genetic influences of behavior
    • e.g. Nest-building behavior in love birds
  7. Selective breeding
    • Separate behavioral variants from within a population
    • Select specific individuals to breed and repeat selection process in each generation (temperament)
    • Behavioral differences that respond to selective breeding must be due at least in part to the differences in the genotype
  8. Natural individual-individual variation
    • Temperament (calm -  reactive) in cattle is heritable
    • Heritability of 0.4-0.5 have been reported
    • Angus more temperamental than Herefords
    • Braham cross more agitated during restraint than shorthorns
  9. Domestication
    Process by which a population of animals become adapted to man and the captive environment by genetic changes occurring over generations and environmentally-induced developmental events reoccurring during each generation
  10. Genetic mechanisms influencing domestication
    • Inbreeding
    • Genetic drift
    • Selection: artificial, natural, relaxation of natural selection
  11. Inbreeding
    • Create random changes in gene frequency
    • Small captive populations
    • Decreased genetic variabilityy
    • "inbreeding depression" - lowering fitness of vigor due to inbreeding: egg hatchability, clutch size, milk yield, litter size
    • Increased risk of genetic disease
  12. Genetic drift
    • Certain alleles become randomly fixed or lost
    • Decrease genetic variability
    • Becomes more severe and more important the smaller the breeding population is
    • "Founder Effect" - When a population is bred from a few originators, genetic drift can be exceedingly severe, and alleles from one or two founders can dominate the resulting population: probably a common component of genetic disease in inbred populations, Known cause of behavior problems in show dogs.
  13. Side effects of selection
    • Behavioral problems
    • Physiological problems
    • Immunological problems
    • Production diseases: diseases caused by systems of management, feeding and breeding of high producing strains of animals
  14. Dairy cattle
    • Selection for increase milk production
    • Lower energy balance in high producers
    • Higher incidence of metabolic disorders
    • More days open
    • Longer calving interval
    • More service/conception
    • More digestive problems
    • More leg injuries
  15. The problem of pleiotropy
    • Over-selection for desired traits can lead to pleiotropic selection for undesired traits
    • Broiler chickens have been intensively selected for breast muscle mass growth, and muscle, carcass weight ratio: rapid growth, altered feeding behavior; altered weight distribution affects gait; growth of skeleton and internal organs does not keep up
  16. Pleiotropy and over selection
    • Reduced cardiopulmonary capacity
    • Cannot withstand much physical exertion, prone to stress-induced mortality as they age...
    • ...so that breeding birds must be heavily food restricted in order to survive to sexual maturity
    • Bone weaknesses, and diseases of - and injuries to - the legs
    • A small proportion of birds may become too lame to reach food and water
  17. Pleiotropy and the selection environment
    • Behavior is easily pleiotropically selected
    • eg. selection for rapid growth of individuals can also lead to selection for aggression
    • When these individuals are housed together aggression may be so severe that it hinders the average growth seen in the group
  18. Genomics/receptors
    • Lots of work happening right now
    • Gene for serotonin receptor HTR2C and feather damage
    • SNPs (single nucleotide polymorphisms) in a number of genes mediation HPA (hypothalamic-pituitary adrenal) axis affects vasopressin receptor 1B and glucocorticoid receptors
  19. Future directions
    • Molecular biology, gene editing
    • What traditionally (be selective breeding) takes 8 generations (24 years in cows) can now be accomplished in a single generation by gene editing.
    • We demonstrated that a sequence associated with horns in dairy cattle could be converted to a natural beef cattle variant that is hornless, providing a strategy to improve animal welfare by genetic instead of physical or chemical dehorning

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